1. Field of the Invention
This disclosure relates to a branching unit for delivering a respiratory gas of a subject.
2. Description of Related Art
Tidal volume (TV) is an amount of an air inspired or taken into the lungs in a single breath. TV is also dependent on the sex, size, height, age and a health etc. of a patient. In general TV also decreases as the size of the patient decreases. In an average healthy adult, TV is about 400-600 ml whereas in an average healthy neonate, that measures 3.5-4 kg and is 50 cm tall, TV is approximately 25-50 ml. On the other hand, in an average premature neonate that measures only 500 grams TV is only about 2-3.5 ml. TV of a smaller patient's is very difficult to measure, but it can be approximated to 4-7 ml/kg, applying a general rule of thumb for approximating the TV of the human lung. In practice the TV of the patient suffering pulmonary system deficiency is normally much less than the approximation gives.
When the patient is mechanically ventilated with a conventional ventilator, an endotracheal tube is placed into a trachea so that it goes through oral or nasal cavity and larynx. The other end of the endotracheal tube is connected to a breathing circuit Y-piece through a luer type connector. If the patient is gas monitored with a mainstream or sidestream gas analyzer, an airway adapter used for sampling the breathing gas that is analyzed by the gas analyzer is normally connected between connectors of the endotracheal tube and the breathing circuit Y-piece. During an inspiration the fresh breathing gas containing higher oxygen (O2) concentration flows into the patients lungs through an inspiratory limb of the breathing circuit Y-piece, the airway adapter, the endotracheal tube and their connectors, then to a trachea, a bronchus, a bronchi, bronchioles and finally reaching an alveoli deep in the lungs, where all the gas exchange actually occurs. Carbon dioxide (CO2) molecules in hemoglobin of a blood flowing in tiny blood vessels around the alveoli are replaced with O2 molecules in the fresh breathing gas through the thin walls of the alveoli. O2 molecules take their place in the hemoglobin, whereas CO2 molecules flow out from the patient within the used expired breathing gas, through the same path as the fresh gas came in during the inspiration. Thus a gas concentration of the breathing gas measured by the gas analyzer is somewhat proportional to the gas concentration in the blood.
A volume in a space between a connection of the inspiratory and expiratory limbs of the Y-piece and the patient's mouth or nose, a beginning of oral and nasal cavities, is called a mechanical dead volume or dead space, whereas the volume in a space between patient's mouth or nose and the entrance of alveoli is called an anatomical dead volume. The part of the lung that is injured or damaged for some reason and does not participate for the gas exchange is called more specific a physical dead volume. It is obvious that as the used breathing gas flows out from the patient's lungs through the expiratory limb during expiration, a part of the used gas newer exits a pulmonary system, as well as the patient side of the breathing circuit, but remains in the mechanical and anatomical dead volume. Then as the fresh gas is inspired in to the lungs through the inspiratory limb the used gas already in the anatomical and mechanical dead volume flows into the lungs before the fresh gas. The used gas fills up some or all of the alveoli depending on a ratio of the dead volume and TV or at least mixes up with the fresh gas decreasing the concentration of O2 as well as increasing the concentration of CO2 in the lungs, which in turn decreases the gas exchange in the alveoli. This means that the larger the dead space, the larger the volume of the used gas, with a low O2 and high CO2 concentration, that flows back to the patients lungs during the inspiration and worse the gas exchange in the alveoli. In other words, if the total dead volume were larger than TV or as large as TV, the patient would not get any fresh gas into the lungs, but respires the used gas back and forth in the dead volume. In practice a diffusion of gases assists the gas exchange over the dead volume little, especially when there is some movement of gases such as high frequency ventilation evolved, but the overall gas exchange in the alveoli would be lethal or dangerously poor anyway.
The anatomical dead volume is almost impossible to reduce, but it is proportional to the size and the physical condition of the patient. The mechanical dead volume depends on a breathing circuit design, defined by the inner diameter of the tubing, connectors and additional accessories. Additional accessories are usually different type of breathing circuit connectors such as a so-called peep saver, T-connector, L-connector etc. used to build up a suitable circuit for the treatment of the patient and to add devices such as gas analyzers, humidifiers, nebulizers etc to the circuit. These additional accessories and devices increase the mechanical dead volume considerably. Obviously the mechanical dead volume is more critical for smaller patients with smaller TV or patients suffering barotraumas etc., which also decrease TV and for this reason many devices cannot be used for the treatment of smaller patients.
The conventional patient side part of the breathing circuit, which is also shown in FIG. 1, usually consists of an endotracheal tube 1, male type luer connector 2, so-called peep saver 3, T-piece 4 used to connect a humidifier, a nebulizer or a similar device (not shown) and Y-piece 5 that connects the patient side part of the breathing circuit to the ventilator through breathing circuit tubing (not shown).
The other end of endotracheal tube 1 enters the patient's trachea (not shown) and the other end contains a male type luer connector 2. The connecter 2 is oftentimes firmly attached to the end of endotracheal tube 1. The conventional, so-called peep saver 3 contains three tubular ports. The first port 31, which is a female type luer connector, can be connected to the male type luer connector 2 at the end of endotracheal tube 1. The second port 32 straight at the opposite side of the first port 31 contains an elastic part 33 with a thin membrane 34 in the middle of it, made of material such as rubber that can be pierced with a catheter. The catheter is used to suck mucus, blood and body fluids from the patient's lungs to keep the lungs open for the gas exchange. The third port 35 is a male type luer connector that is adjacent to and in sharp angle relative to the second port 32. The conventional T-piece 4 also contains three tubular openings. The first port 41 of the T-piece 4, which is a female type luer connector, can be connected to the male type third port 35 of peep saver 3 or the male type luer connector 2 at the end of endotracheal tube 1. A second port 42 of the T-piece 4 is used to connect a humidifier, a nebulizer or a similar device in to the breathing circuit so that the fluid flows through an opening 43 in the port 42 of the T-piece 4 into the breathing gas flowing by the port. The opening 43 can be closed with a cap 44 to prevent the pressure and the flow inside the breathing circuit to escape through the opening when the connectable device is not used. A third port 45 is a male type luer connector. The conventional Y-piece 5 contains three tubular ports as well. A first port 51, which is a female type luer connector, can be connected to the male type luer third port 45 of the T-piece 4, the male type luer third port 35 of the peep saver 3 or the male type luer connector 2 at the end of endotracheal tube 1. An inspiratory limb 52 of the Y-piece 5 connects to a ventilator through an inspiratory tubing to carry inspiratory fresh gas through the circuit into the patient whereas an expiratory limb 53 connects to the ventilator through an expiratory tubing to carry expiratory gas out from the patient. If a breathing gas analyzing is desired the adapter consisting male and female type luer connectors is usually connected between the connector 2 of endotracheal tube 1 and the peep saver 3 or the peep saver 3 and the T-piece 4 or the T-piece 4 and the Y-piece 5 (not shown in FIG. 1).
All of the male and the female type luer connectors in the circuit are standard size and all the males and the females connect to each other regardless of which connectors or pieces are connected together. Although all the pieces and connectors can be placed freely into different locations in the circuit the peep saver 3 should be connected always to the connector 2 of the endotracheal tube 1 to ensure that the catheter has the shortest and free entrance into the patient's lungs. The free placement of different parts thus causes a disadvantage for misplacing the parts.
Conventional humidifiers and nebulizers are big and clumsy thus they are normally connected between the inspiratory lines close to the ventilator. If the nebulizer is desired closer to the patient, to achieve better delivery efficiency, it is connected to the T-piece. Because of the device size the T-piece is also relatively big and its dead volume large, approximately 10-15 ml. Furthermore as the device is connected to the T-piece the large dead volume of the device itself, which may be tens of milliliters, is also added to the total dead volume of the circuit. For this reason the T-connector is usually placed into the circuit for that time only to enable the delivery of fluids into the patient's lungs. The disadvantage is that the circuit is opened twice for each treatment, as the T-piece is connected on and off, and the pressure and the flow inside the circuit escape. Especially the pressure drop inside the circuit is dangerous for the unhealthy lungs since the lungs and the alveoli deep in the lungs used for the gas exchange collapse each time the circuit is opened. During the collapse the gas exchange is decreased considerably and the recovery from the collapse may take even several hours and usually needs expensive and difficult further medication. Further disadvantage is the opening 43 where the pressure and the flow escape similarly each time it is opened. Another disadvantage, especially with nebulizers, is the location of the second port 42 of the T-piece 4. Most of the nebulizers generate the aerosol so that the speed of the fluid drops is high. As the drops come out from the nebulizer and through the second port 42 they hit into the wall between the first port 41 and the third port 45 at the opposite side of the nebulizer exit. Thus many of the generated fluid drop newer reach the patient's lungs, but turn into a liquid in the circuit again and cause problems for the patient and decrease the delivery efficiency.
The peep saver is continuously used at least with pediatric and adult patients and the lungs are usually sucked empty of body fluids with a catheter through the peep saver many times per day at least in ICU (intensive care unit). Although its advantage of saving the pressure and the flow inside the circuit during the treatment the disadvantage is the large dead volume, approximately 10-15 ml, it adds to the circuit. Similarly the connector 2 of the endotracheal tube 1 as well as the first port 51 of the Y-piece 5 both increase the dead volume of the circuit by approximately 2-3 ml thus the increase together is approximately 4-6 ml.
Thus when using the patient side part of the breathing circuit, as also shown in FIG. 1, the overall size and the weight of the circuit is huge not to mention the very large overall dead volume, approximately 25-35 ml.
Also the number of male and female connections, each causing step like change into the breathing circuit flow path, as well as large volumes of each connector and piece, cause turbulences into the gas flow that in turn mix the fresh gas flowing towards the patient and the used gas flowing out from the patient decreasing the gas exchange in the lungs.